Syrian rebels appear to have captured the northern city of Raqqa, in one of the biggest gains of their two-year revolt against President Bashar al-Assad.

In another blow to the Syrian government Monday, suspected al-Qaida militants killed 48 Syrian security personnel inside Iraq, as the Syrians were traveling to a border crossing to return home.

In Raqqa, activists posted videos on the Internet showing residents celebrating the rebel victory on Monday, tearing down a banner of Assad over a central square and toppling a statue of his father and predecessor, Hafez al-Assad.

Activists said some government troops remained holed up in a military compound in the city. Sunni-majority rebels opposed to Assad's 12-year minority Alawite rule have been trying to oust his forces from predominantly-Sunni Raqqa for weeks.

Uprising milestone

If the rebel takeover is independently confirmed, it would mark the first Syrian provincial capital to fall into opposition hands. Syrian rebels also hold parts of the major cities of Aleppo and Homs, and some suburbs of Damascus.

Syria observer Joshua Landis of the University of Oklahoma said Raqqa is strategically important because it is located on the highway to the major northeastern towns of Qamishli, Hasakah and Deir el-Zour.

Landis, who authors the blog Syria Comment, said Raqqa also is near a major oil producing region and is a farming hub because of its proximity to Assad Lake and the Euphrates River.

"This is a Sunni region [that] has been very faithful to [Assad's] Baath party throughout the years," he said.

"But [Raqqa] has been extremely poor and underprivileged. It has not gotten a lot from the state. It hoped that the building of Assad Dam along the Euphrates River would bring a lot of irrigation, new farmland and riches. None of that really panned out."

Government resistance

Despite the setback in Raqqa, pro-Assad fighters remain in control of central Damascus, his seat of power, and other parts of western Syria populated by his fellow Alawites.

Landis said Assad's army has been trying to consolidate its hold of those areas.

"The Syrian military is attacking around [the central city of] Homs and to the north of Latakia. It is fattening up the areas under its control, particularly around the Alawite mountains and on the highway from Damascus up toward Homs and to the west. But it is relinquishing much of the territory around Aleppo and to the east."

In other amateur videos posted on the Internet Monday, rebels in Homs appeared to fight back against a government offensive, while opposition fighters on the western outskirts of Aleppo claimed the capture of a police academy.

Conflict spreads

Dozens of Syrian security personnel who entered Iraq last week were ambushed as Iraqi authorities were escorting them back to Syria. Iraqi officials said the attack killed 48 Syrians and at least seven Iraqis, and they blamed it on Sunni al-Qaida militants.

The Assad loyalists had crossed into Iraq via the northern border terminal of Yaarabiya to escape Syrian rebel attacks. Iraqi security forces were transporting them to the southern border crossing of al-Walid when the ambush happened in Iraq's Anbar province.

Iraq's Shi'ite-led government publicly has refused to take sides in the Syrian civil war. Baghdad said it granted entry to the pro-Assad forces as a humanitarian gesture and warned all parties in Syria not to bring their fight into Iraq.

Islamist alliance

Landis said the ambush appears to be the work of al-Qaida's Iraqi branch working in tandem with Syria-based Sunni militants such as Jabhat al-Nusra.

"Most of the big tribes along the border have members on both sides, in Iraq and Syria. They are helping each other with arms, they are helping each other attack Syrian army elements in that region," he said.

"[Syrian Sunnis] are working hand-in-glove [together] with Iraqi Sunnis against the Shi'ite governments in Iraq and Syria, both [of whom] are allied with Iran."

Assad's Alawite sect is an offshoot of Shi'ite Islam. Iraq's Shi'ite Prime Minister Nouri al-Maliki has warned that a rebel takeover of Syria could embolden Iraqi Sunni militants trying to destabilize his government.